Switches have been used for communications and network applications. A switch fabric that forms interconnections may be constructed from a variety of devices, such as pass transistors, gates, store-and-forward nodes, etc. However, these are typically digital devices that pass digital signals.
More recently, analog signals have been employed for higher-speed signaling. Differential analog signals allow a small voltage change to be used for signaling, while digital signals require a much larger voltage swing and thus require more energy to charge and discharge capacitances. The smaller voltage changes needed by differential analog signals often allows for faster signaling than digital signals.
Analog signals are significantly degraded when passing through a switch fabric. The impedance of transistors in a switch fabric may be small enough for slower digital signals, but for faster analog signals the impedance is too large, causing signal degradation at high frequencies.
The lengths and loads of various paths through a switch fabric may vary, causing mis-matched loads and variable delays on differential signals. Without the large noise margin of digital signals, analog signals can be ruined by such variable path loading. Thus either digital signals are used in switch fabrics, or larger-swing analog signals are used. Analog signals such as low-voltage differential signaling (LVDS) may only swing by a few hundred millivolts and are sensitive to such path mis-matches.
What is desired is a switch fabric for switching small-swing analog signals. A multiplexer and demultiplexer for analog signals is desirable that can be used as a building block in a larger switch fabric. A mux/demux that cancels loading effects and regenerates analog signals is desirable.